The invention relates generally to power conversion circuits and, particularly to a system for detection of a ground fault in a high resistance ground network system.
Wide ranges of equipment utilizing various power converter circuits are known, such as electric motor drive systems used in factory automation systems, power generation systems and so forth. Typically an electric motor drive is connected to a power source, most often the power grid, and operates to provide electrical power to a load in a controlled manner.
In voltage power conversion circuits, electrical power is converted from an AC power source into direct current (DC) power via a power converter. The DC power is then converted via an inverter coupled to the converter through a DC bus into AC power with controlled frequency, phase and amplitude, which may be applied to drive an external load such as the electric motor.
Typically, it is desirable to detect whether a drive is operating in a ground fault on a high resistance ground network so that the ground fault may be cleared before it causes failures in components of the circuit. In operation, the bus voltages increase substantially during a ground fault resulting in high voltage stresses in the components such as motor and cables of the system. Because of the high resistance that normally exists during the ground faults on high resistance ground networks, the fault current is small and therefore often negligible thereby making it difficult to reliably separate such faults from large changes of the load.
Most conventional techniques for detecting ground faults on high resistance ground networks are based on simplified impedance models for the transmission line. However, these techniques lack sufficient accuracy when applied to systems containing power converters. Another way of detecting ground faults on high resistance ground networks is by measuring output phase to ground voltage in the circuit. However, such technique is complicated and can identify only output phase to ground fault.
Accordingly, it would be desirable to develop a system that detects presence and location of ground faults on high resistance ground networks in power conversion circuits during and/or prior to operation of such systems.